His point was that AAA games are categorically repetitive, too. I saw a trend start with Resident Evil 4's camera. After that it was Gears of War, and then it was Dead Space (which had the sole distinction of having a horror paintjob, which it's shed recently only to be that much more similar to other games).
To the TC: They're sidescrollers, but that describes presentation moreso than other aspects of a game. Cave Story and Braid aren't very similar gameplay-wise. I think it's chosen because it's an easy look to achieve (easier than 3D modeling, or isometric views in which you're dealing with perspective 2D art, and that can be a beehive), and is more conducive to story-telling than something like the Tetris format. Notice how a lot of the outstanding Indie games have a significant story element.